Home » The Rotary Range-Extender Mazda MX-30 Could Be The Weirdest New Car On The Road

The Rotary Range-Extender Mazda MX-30 Could Be The Weirdest New Car On The Road

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Of all the electric vehicles on sale right now, none have evoked as much of a collective “Huh?” as the Mazda MX-30. With its crossover stance, tight coupe-like body, rear-hinged “freestyle” double-doors and a battery good for only about 100 miles of range, it has all the chaotic energy of that guy who shows up to class late, asks to see your notes and says “What’d I miss?” every. Single. Day.

But unlike the guy who had no business taking an 8 a.m. class, Mazda has no choice but to electrify, and that’s a tough proposition for a small, independent automaker that isn’t flush with investor cash—one of the last, really. So can Mazda’s only EV (for now) be more than it is? It says yes, and one answer for now at least is bringing back the rotary engine as a range extender, not unlike the Chevrolet Volt or the BMW i3. And though a “new rotary engine” has been rumored since the Fast & Furious movies were still about street racing, Mazda’s confirmed it’s actually doing this.

Now, via a patent scoop from CarBuzz, we can see how unusual this new rotary range extender for the MX-30 will really be. And the end result—all that stuff I listed in my lede, plus the magic spinning triangle engine—could make this the weirdest new car on the road. (Seriously, what could be weirder than this right now? I’ll wait.)

The site says this new Mazda rotary aims to be significantly more efficient than its notoriously not-so predecessors by adding something akin to variable valve timing. I’m just going to quote the article rather than screw this up by attempting to explain it myself:

According to the patent, the first step towards optimizing the new rotary’s efficiency is by employing a dual-intake port arrangement. The rotor tip passes the primary port first before passing the secondary port a little further in its rotation. The secondary port prolongs the “intake stroke,” allowing more air into the combustion chamber in high-power demand situations.

However, the secondary port also interferes with low-speed efficiency, so Mazda added a throttle valve to close it off in low-power conditions. This has the same effect as altering the valve timing on a piston engine and improves the rotary’s breathing efficiency over a wider speed range. Following along? Good. Now the next part is where it gets confusing.

Screen Shot 2022 12 14 At 10.37.32 Am

Fascinating already. And that “next part” refers to the electric motor; it’s fed by the EV’s high-voltage traction battery and can speed up or slow down the rotary engine as needed to optimize the intake into the combustion chamber. [Ed note: The patent, US 20220381190 A1, actually mentions that the slowing or speeding of the rotary engine could happen via a separate “assist motor” independent of the generator, though this assist motor, the patent makes clear, isn’t needed and is likely only mentioned to cover the invention broadly -DT].

As that story notes, the rotary engine here is just used to generate electricity, not drive the wheels themselves. But it’s a unique application of something that’s historically important to Mazda, and while it’s not the same as a new RX-7, it’s great to see this company trying something so different.  Here’s a basic description of the patent from document’s abstract:

An electric vehicle includes an engine for electricity generation in which closing timing of an intake port maximizes intake air charging efficiency in a specific revolution speed region, a sensor which outputs a signal related to a revolution speed of the engine, a controller which drives the engine at a revolution speed based on the signal of the sensor, a requested electricity generation amount being satisfied at the revolution speed, and a motor which applies a positive or negative torque to the engine. When the engine is driven in a revolution speed region other than the specific revolution speed region, the controller uses the motor to apply a positive or a negative torque to the engine in an intake stroke to change the closing timing of the intake port to increase intake air charging efficiency.

[Long Ed note: Here’s a look at the control logic. You can see that, based on how much electricity is needed to keep the battery charged to satisfy the customer’s needs (i.e. run the electric motor and accessories), the rotary engine is set to a certain operating point. A computer is constantly reading engine RPM, determining intake air flow speed, and adjusting intake timing. On a typical piston-engine, this adjustment of intake timing would happen via a camshaft phaser — basically as stepper motor on a camshaft; a Wankel rotary engine doesn’t have a camshaft, so it has to adjust intake timing/duration another way.

Screen Shot 2022 12 14 At 11.11.21 Am

The patent breaks it down:

The intake closing timing of the rotary engine is set such that the intake air charging efficiency becomes a maximum in the revolution speed region in which the use frequency of the rotary engine is highest. In the control map, the revolution speed region in which the use frequency of the rotary engine is highest is a part around the center in a use revolution speed range of the engine, and here, the assist torque is zero:

Screen Shot 2022 12 14 At 12.27.24 Pm

You can see at low RPMS, there’s positive assist torque, and at high RPMs, there’s negative assist torque. At that optimal RPM that will see high usage, the “assist motor” doesn’t apply a torque.

The patent continues:

In order to make the intake closing timing earlier when the revolution speed of the rotary engine becomes lower than the revolution speed region in which use frequency is highest, the assist torque is set to a positive torque. In order to make the intake closing timing later when the revolution speed becomes higher than the revolution speed region in which use frequency is highest, the assist torque is set to a negative torque.

If that’s still not clear, maybe this and the diagram below will help a tiny bit:

In a case where the intake closing timing of the rotary engine is later than the optimal closing timing, the assist motor performs “power running” and thereby temporarily applies a positive torque to the rotary engine in the intake stroke. Accordingly, the revolution rate of the rotary engine is temporarily made higher, and the intake closing timing of the engine is made earlier. Further, in a case where the intake closing timing of the rotary engine is earlier than the optimal closing timing, the assist motor performs “electricity generation driving” and thereby temporarily applies a negative torque to the rotary engine in the intake stroke. Accordingly, the revolution rate of the rotary engine is temporarily made lower, and the intake closing timing of the engine is made later.

Screen Shot 2022 12 14 At 12.46.59 Pm

I’m going to be honest: I’m a little bit confused by the way this patent is worded, so engineers please chime in. But it seems to me that optimal intake timing occurs at a given RPM (the one the engine will run at most of the time) but there are certain scenarios (presumably when the battery is at a really low state of charge and draws lots of load from the generator, or the opposite where the battery is full/regen?) that would operate that engine outside of its optimal intake timing point; an electric motor lowers or raises the load on the engine to bring intake timing closer to optimal — that’s how I read this, though again, it’s a patent document, so not the clearest on earth. And also, I’m no powertrain engineer! -DT]

Right now, the MX-30 is only sold in California due to regulatory issues there, and it seems to have been sold out for a while. No word yet on when this range-extended MX-30 is due to come out, but it could inject some new life (and hopefully more of a national presence) into this unique machine, paving the way for Mazda to launch at least three new EVs by 2025. Though Mazda is small and definitely in catch-up mode on the EV front, it’s got a bunch of partnerships planned with several Japanese technology firms and wants electric cars to make up a quarter of its sales by 2030.

In the meantime, here’s hoping the MX-30 with this unusual rotary engine finally hits the streets soon. If this company can pull that off, surely I can succeed in finally getting David Tracy to buy an FB or FC RX-7 so he can bring years of glorious rotary wrenching content your way.

Images: USPTO via CarBuzz

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57 Responses

  1. This sounds great. I remember when the Jaguar C-X75 was first shown they claimed it would be electric powered with a pair of tiny jet engines acting as the range extender. That would’ve been awesome.

  2. I’m confused… why is this needed? I’ve always assumed that the great advantage of having an electric car with onboard generation (via gas engine) would be that the engine could be designed to only/always run at the most efficient RPM where energy generation is balanced with gasoline usage. In other words, a normal gas engine needs to be designed with certain power and torque across a wide range of RPMs. This shouldn’t’ be necessary if the engine only serves to drive a generator, so you can focus the design to be efficient within a narrow range.

    Now Mazda is adding complexity… is it necessary? Am I totally wrong on this?

    1. The issue is that even though the motor is just being used as a generator, it still needs to run over a range of speeds and loads to somewhat follow the power demands of the vehicle. This is down to the inherent inefficiencies of recharging/discharging a battery – you take about a 10% hit on charging, making efficiency when running the engine that much worse unless you can try to match up with the vehicle’s power demand and send most of the power required to drive the vehicle directly from generator to traction motor. This is why the Volt had a drive mode that essentially coupled the engine to the wheels at higher speeds, going from a pure series hybrid to a more conventional setup because it was more efficient. Therefore, the rotary range-extender will need to operate over a range of speeds and loads, it just won’t be as large of a range if there was a geared transmission between the engine and the wheels, and it won’t be forced to change speed and load as quickly.

      With that in mind, this is basically a controls-level tweak to slow down or speed up the engine speed just during the intake stroke to effectively get the benefits of cam phasing to make the engine more efficient over that range of speeds and loads. The multiple ports is just background, and is equivalent to different cam profiles that can be switched between (and is old news for rotaries – they’ve been doing this since the 2nd generation RX-7 with 4-port turbo and 6-port NA engines).

    2. More than likely, it is smoke and mirrors, much like the Volt’s magic “serial” hybrid system, which is actually parallel, as admitted by Lutz on its reveal, but completely forgotten about immediately thereafter. From the Volt:
      “Dual-motor extended – The electric motors are used again in dual configuration with increased efficiency at higher speeds. Additionally, the gasoline engine contributes propulsion power via the planetary gear. While power is drained from the battery the amount is less than in mode 2 for the same propulsion power, thus extending the range.”
      This is exactly what all hybrids do, with a higher drive range than most (70mph versus 47mph). I am thinking that is what might be going on here.

      1. A series hybrid is not good for gas mileage. Why would you want to convert power twice and throw away energy when you could add some clutches and skip the conversions?

        The Fisker Karma operated as a simple series hybrid and it got *awful* mpg (after it ran through its EV range).

        The Volt’s ability to switch between pure EV, series hybrid, and parallel hybrid modes was actually really slick engineering. It gave you better mpg.

    3. You and I have the same confusion. I thought the beauty of this was that rotary engines work very efficiently within their preferred RPM band, so you could just run it there to charge the battery. This…just adds complexity that will make it difficult to service, especially once this engine is inevitably out of production in just a few years.

    4. If only Mazda had already designed and engineered a weird combustion engine that runs incredibly efficiently at steady torque/RPM to use as a generator without all the nonsense of a rotary. Say, maybe a piston engine that happened to use compression ignition, but still had spark plugs to control that compression ignition. Call it spark-controlled compression ignition, or SCCI. And maybe they could even slot that engine into their standard nomenclature–maybe SKYACTIV-X? I dunno, might just work for a PHEV.

      1. Did that ever actually come out or was it vaporware? They talked about it and talked about and kept saying ‘Any day now!’ and it just never seemed to materialize.

        1. It exists in Europe. Getting the nitrate emissions low enough to comply with US regulations has thus far proved impossible without cutting power to unacceptably low levels.

      2. The rotary motor has the big advantage of its small packaging, especially if it’s just going to be feeding an alternator. And if it’s going to be run by a computer it can probably do so about as efficiently as physically possible.

        I think this is some good lemonade that Mazda is making out of the market transition to EV lemons the market has served them. Assuming they don’t take forever to release them and don’t have too many glitches at launch (something something never buy v1 of a new technology).

      3. I agree but that engine would be overqualified for the job (and thus likely too expensive).It’s made to be economical over a wide range of revs,something that isnt needed on a hybrid.

    5. Probably, the control circuit compensates for the variable drag on the rotor depending on the load from the generator part, in order to maintain the most efficient air/fuel charge ratio and engine speed.

      At least that’s how I read it.

      And I want one of these. Badly.

      1. I’ve wanted one since they first announced it and I was so disappointed when they just brought the EV out and scrubbed mentions of this. This looks more complex than I had envisioned, but I still want it. Probably even enough to try to order one in California if necessary (though I hope they at least hit a few more states with the PHEV.

        1. I want one, want to hear more about MPG, range, and performance, but the whole idea is so cool. I think the car looks good. Carrying around a light and compact range extender makes sense. Would love to test driving it

      2. Yeah, that’s how I interpreted it too.

        It sounds like they’re using the assist motor torque as a proportional controller to make up the difference between the torque the engine would otherwise produce and what’s required to maintain a steady engine RPM (and max. efficiency).

        1. Is this solution partly about using one electric motor only? Where something like a prius has always used two,even though not strictly necessary.

          Either way i have huge doubts the intake tricks will make the rotary more economical than a piston engine.It’s starting point is far too low.
          And i hope i’m wrong of course!

  3. Patent descriptions are so tough to follow that it’s hard to tell if this is a similar arrangement (the variable valve timing at least) to the last two normally aspirated production rotary engines. Both the 13B-MSP (commonly known as the RENESIS, or the engine that died a lot) and the 13B-DEI (in the FC or second generation RX-7) were six port arrangements. There were four primary ports and two auxiliary ports in total. The auxiliary ports were activated by backpressure from the exhaust in the early 13B-DEI and positive pressure from an airpump in the later 13B-DEI and the 13B-MSP. The thinking was exactly the same then. Having all six ports open during low engine speed killed torque (what little the engines had) and was better for high speed power.

    1. Looking at the drawings and descriptions, it seems to be a 4-port engine, not a 6-port like the ones you mentioned. I think they’ve done away with the vacuum/air-actuated (FC) or stepper-motor (Renesis) sleeve-valved 5th & 6th ports, and just have a 4-port engine where the ports are controlled via independent throttle bodies. This is more similar to the FC turbo 4-port 13B-T engines that have the staged throttle bodies feeding into separate manifolds and runners for the ports on the inner iron vs the outer irons (also implemented for the 2 primary ports on the outer irons in the Renesis with a barrel valve in the LIM).

      My guess is that the discussion on ports is just background, while the novel part of the invention being covered by the patent is using the electric generator to selectively slow down or speed up the engine during the intake stroke to get a cam phasing-type effect in addition to the switchable valve profile effect (similar to VTec, yo!) that the different ports allow.

  4. The oil smokes white on the mountain tonight
    Not another carbon footprint to be seen
    A kingdom of isolation
    And it looks like I’m the queen
    The combustion is howling like this swirling storm inside
    Couldn’t keep it in, heaven knows I’ve tried
    Don’t let them in, don’t let them see
    Be the good Mazda you always have to be
    Conceal, don’t feel, don’t let them know
    Well, now they know
    Let it go, let it go
    Can’t hold it back anymore
    Let it go, let it go
    Turn away and slam the rear coach door
    I don’t care what they’re going to say
    Keep the battery range on
    The smoke never bothered me anyway
    It’s funny how some distance makes everything seem small
    And the fears that once controlled me can’t get to me at all
    It’s time to see what I can do
    To test the limits and break through
    No right, no wrong, no rules for me
    I’m free
    Let it go, let it go
    I am one with the wind and sky
    Let it go, let it go
    You’ll never see me cry
    Here I stand and here I stay
    Keep the battery range on
    My power flurries through the air into the ground
    My soul is rotating in blown seals all around
    And one thought blows by like an oily blast
    I’m never going back, the past is in the past
    Let it go, let it go
    When I’ll rise like the break of dawn
    Let it go, let it go
    That perfect Mazda is gone
    Here I stand in the light of day
    Keep the battery range on
    The smoke never bothered me anyway

      1. Reindeers are better than people
        Sven, don’t you think that’s true?
        Yeah, people will beat you
        And curse you and cheat you
        Every one of them’s bad except you
        Oh, thanks buddy
        But people smell better than reindeers
        Sven, don’t you think that I’m right?
        That’s once again true, for all except you
        You got me, let’s call it a night

    1. Is it the flood prone way it starts?
      Or the exhaust that sounds like farts?
      Or the tear-shaped, ear shaped weirdness of its doors?

      and even though it handles well, the title’s brand all to hell
      But you’ll never hear a sound quite like 9,000 rpm and more!

      So she’s a bit of a fixer-upper
      so she’s got a few flaws
      It’s peculiar engine, the need for high revving
      that requires breaking traffic laws

      So she’s a bit of a fixer upper, but this were certain of
      you can fix this fixer upper with a little bit of love!

    2. We don’t talk about Wankel, no no
      We don’t talk about Wankel…
      It’s was my RX-8 (it was our RX-8)
      We were going racing
      and there wasn’t a light on the dash
      (no lights allowed on the dash)
      The Wankel starts in with its elliptical spin and (THUNDER!)
      Who’s oiling this rotor, you nor I?
      (The sorry apex seal was goooooone)

          1. He’s moving to California, so hopefully two things happen: 1) He changes his ways a little bit and doesn’t buy the absolute worst example of what he wants (please stop laughing) and 2) It’s California, the percentage of absolute rust boxes has to be lower, right?

          2. When David applies a wrench to a non-rusty Californian bolt, gives it a twist and it un-threads without copious amounts of PB-Blaster, snapping off, or just plain not budging, the rusts enthralling spell over David may be broken.

            My English teacher would probably be appalled at my run-on sentence. Sorry Mrs. Z.

      1. I’ve literally been waiting years for this. Everytime I read you’ve got a new shitbox, I’m hoping it’s finally an RX=7. DT in CA needs an [shitbox] RX-7

  5. Mazda serves us attractive, fun to drive, high quality cars with a unique twist. Sadly I think they will go bankrupt within the span of 10 years unless they turn their full weight and commitment to EVs. Hybrids made sense 20 years ago. They make little sense today, and zero sense in three years.

    While the CX-30 makes little sense to most people with its minuscule range, it did sell out in the US. That should tell everyone an electric Mazda will be very attractive, when even an imperfect one sells this well.

  6. Ok, I’m pretty sure I get the swing of what Mazda is up to here. They are using an electric motor to act as a cam phasor so they can either slow down the rotor in times when more air/fuel is needed such as producing higher torque (which the rotary is bad at unless under forced induction) or speed it up when they need higher speed and want to reduce fuel/air usage (like when they want to run the generator flat out at top production). This would be helpful when the generator is under heavy load, like when it’s trying to recharge the battery system. This would also help the generator under starting conditions when the rotor (of the generator) has the highest current draw under a locked rotor condition (LRA). Basically, they are advancing and retarding the fuel/air ratios using rotor rpm to try to keep they rotary engine as close to the electric generator as possible to produce the most efficient power conversion possible.

  7. I wonder if they’re using the electric motor/alternator to control the engine RPMs because it takes some time to move the throttle valve on the second intake? ie they’re controlling how fast it revs up (or down), so that they can control the second intake more accurately.

  8. The linked article is actually pretty easy to understand.Or their explanation at least.
    The electric motor is physically slowing (or speeding up) the rotary engine DURING THE INTAKE STROKE.
    This will obviously create bizarre vibrations but those should be easy enough to deal with.

  9. I’m eagerly awaiting the release of a sub-2500 lb electric MX-5 coupe. If aerodynamic drag reduction and weight reduction are the focus, then a large battery pack is not needed for competitive range. The potential to have a sub-$30k EV that can rip off sub-4-second 0-60 mph times and out-corner cars 10x its cost is there.

  10. I’m having trouble seeing the appeal. Rotary engines are very cool, thanks to their compact size allowing better engine placement for better dynamics, their awesome sound and rpm potential, and their tunability.
    When used as a range extender, the engine will drone at a varying set rpm and will not be linear with vehicle speed or throttle input, but rather charging demands. It will be annoying, and they will try to mute it as much as they can.
    Engine placement will just be where ever they can fit it, given all the extra crap they need to jam in there for this vehicle’s 2 powertrains.
    The new experimental tech in this engine could possibly result in less atrocious fuel economy, emissions and reliability, but it could and likely will make it less reliable. Why on earth would you use an engine known for poor economy and emissions as a range extender? Engineers, please chime in.
    Furthermore, why develop a new range extender EV when previous ones have been such epic market failures?
    A full EV with fake rotary sound through the speakers would be pretty stupid, but it would be a better vehicle in every way.

    1. “Why on earth would you use an engine known for poor economy and emissions as a range extender? Engineers, please chime in“

      I’m an engineer. Previously worked on range-extended electric vehicles (REEV).

      Imagine you plug in your EV every night, and do all your daily driving in EV mode, then a few times a month/year you need to do a 600 mile road trip. That’s when you use your range extender. You can live with the inefficiency of the Wankel if it’s small and light enough to be a more efficient solution than a piston ICE you’d be lugging around all the time instead.

      I’ve been in prototype REEVs when the piston RE starts up, it’s an NVH nightmare. A Wankel cuts the vibration way down (I had an FC RX7 for a while, sooo smooth) so that’s a lot of space and money saved on NVH. You’ll want a nice big muffler, but that’s crushable so can live in a crumple zone, which you can’t use as space for batteries, motors, fuel or people.

      It’s a smaller, lighter solution that is more energy efficient over the life of the vehicle. But only if your daily use is within battery range (which it probably is for most people) and you actually plug it in to charge.

      1. “Imagine you plug in your EV every night, and do all your daily driving in EV mode, then a few times a month/year you need to do a 600 mile road trip. That’s when you use your range extender.”

        Of course we’ve all heard the old trope of why EVs are no good because you can’t take that 600 mile road trip once a year. Many people drive much more vehicle than they need just for that once of twice a year when they tow a boat or take a long road trip. People should buy and drive what they like of course.

        “You can live with the inefficiency of the Wankel if it’s small and light enough to be a more efficient solution than a piston ICE”

        Wankels don’t have the ability to burn fuel as efficiently as a piston engine, meaning lower power density and high emissions. They can make great power for they’re physical size, but the wankel being a light weight engine is a myth. It would likely weigh more than a piston engine at the same power level.

        Don’t get me wrong, I love and appreciate Wankels, I just think there is a lot of myth surrounding them.

        The NVH is a great point, as that’s really a big part of my disdain for range extenders. A Chevy Volt or i3 with the range extender running is a miserable thing.

        Thanks for sharing your insight. I still don’t like it, but I’m no crossover enthusaist anyway. Hopefully people will buy this and then Mazda will have more money for Miata-like things.

  11. Part of my mind still thinks Mazda engineers / corporate came up with this to try to mess with VW. VW gave them impossible Dieselgate performance figures Mazda tried to match with SkyActiv – Diesel. I wonder how much money they wasted chasing down that rabbit hole?

  12. It is interesting that they are using an electric motor to selectively slow down or speed up the rotor during the ‘intake strokes’ of the engine to change the port opening times… sounds violent to me, but modern engine mounts do wonders.
    The thing that kills Wankel engine efficiency is their truly abysmal combustion chamber surface area to volume ratio, so they have a *lot* of combustion heat loss. When I heard they were going to use a rotary as a range extender, I thought it might have merit – rotaries are very light and compact for their power, so you can minimize weight and passenger/cargo volume penalties of having the range extender in there. My thought was that they’d get around the combustion heat loss problem by making the engine tiny and only running it at absolutely screaming RPMs, limiting heat loss by making cycle times absurdly short. Obviously you have a friction tradeoff there… Does anyone know the power/displacement/rpm range of the engine they’re proposing for the CX30?

  13. I just want to point out that all electric cars are technically rotary powered. The only electric piston motor I can think of off hand is a loudspeaker.

  14. I mean, I haven’t read too much into it, but aren’t most rotary reliability issues partially user error? i.e. flooding when shut-off cold, lugging the engine, etc. etc. so putting the control system in the hands of a computer seems like the most likely way to make it a (more) reliable powerplant. At the end of the day, though, I don’t think the rotary has any chance of being any more optimized than it already has been by Mazda, so whatever foibles it still has will probably never be truly resolved. It will be interesting to know if they found a material that can actually be used as an apex seal or if you’ll be expected to refill the oil of your PHEV every 800 miles.

    1. The main issue has always been the apex seals, as far as I’m aware. It seems damn near impossible to engineer ones that will last for any reasonable length of time.

      1. I think newer designs with silicon nitride ceramic seals may have ameliorated that issue somewhat. One of the reason I want one, is I want to look at how it’s built.

        Getting a serious Jones here.

      2. The main issue is really that the apex seals destroy the engine housing when they go bad (ask me how I know). What usually causes them to die is carbon build up around the rotor tips so they can’t effectively move and they shatter. Good engine management will relieve this somewhat, but as something that burns lubricating oil by design carbon build up is almost impossible to avoid.

      3. Apex seals certainly kill engines, but their contribution to rotary engine death (at least in later incarnations) is dramatically overblown. From personal experience and observation, primary causes of death are owners who don’t know how rotaries work and don’t take care of them properly, and tuner bois who feel like they need to MOD ALL THE THINGS and turn a finely tuned machine into a turd bomb.

  15. Or they could just use the liquid piston design that the military is looking to use for portable generators…., or just like a regular piston engine that won’t burn oil, whichever.

    I do think that PHEV’s time is not over, if a hybrid can achieve over 60mpg it’s approaching fossil fueled power plant levels of efficiency all on it’s own, with less weight and cost than a full on battery EV, and a decent heater too.

    Until this fusion thing really starts going, BEVs are still tethered to their power generation. Maybe not at home for the solar or those that can pick their providers, but definitely with public charging.

  16. Whatever happened tot he Liquid Piston reverse wankel design? seems like if that is available in diesel for the military, it might be something for others looking for more efficient and simple hybrids.

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